As a wide range of different types of advanced components have become cheaper and easier to produce, more user devices used in our daily lives are equipped with one or more micro processors and sensors and are also provided with connectivity capabilities enabling connectivity via wireless networks.
One way of utilizing the possibility that more and more devices can be constantly connected to the Internet, that they can be equipped with up to a multitude of sensors capable of measuring and monitoring their environment, and that they also can be able to connect to each other through various types of short or middle range radio technologies, is to use information decisive of the distance between the devices to alert its owner of unusual or unexpected situations.
Two devices, both having e.g. Bluetooth connectivity capabilities, may e.g. be configured such that one of them can detect when they become separated from each other. Such a feature has been used in Bluetooth equipped wrist watches which are capable of connecting to a users mobile phone. When such a Bluetooth connection is interrupted, due to that the wrist watch is located out of range from the mobile phone, the watch alerts the user that he/she may be about to move away from the mobile phone.
However, when a short or middle range connection, such as e.g. the Bluetooth connection mentioned above, is constantly kept on between mobile devices for the purpose of detecting when they have been separated out of range from each other, the battery of one or both of the devices will most likely be drained quickly.
In addition, many mobile devices, such as e.g. mobile phones, are not by default visible to each other, such that they can be detected as a short or middle range connectivity device, and therefore one of the devices can only be detected by the other device to determine proximity on occasions when it has actively been made visible by the user.